GE 745 - 5.4.5 Harmonics; 5.4.6 FlexCurves

5–38 745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
S2 SYSTEM SETUP CHAPTER 5: SETPOINTS
• RESISTANCE INCREMENT PER TAP: Enter the resistance increment that the 745 will see
for each tap increment. The maximum resistance value for the top tap is 5 KΩ.
5.4.5 Harmonics
PATH: SETPOINTS  S2 SYSTEM SETUP  HARMONICS
The 745 calculates the individual harmonics in each of the phase current inputs up to the
21
st
harmonic. With this information, it calculates an estimate of the effect of non-
sinusoidal load currents on the transformer rated full load current. These calculations are
based on ANSI/IEEE Standard C57.110-1986, and require information that is often only
available from the transformer manufacturer’s test report, including the three-phase
resistance of each winding and the load loss at rated load. The harmonic derating factor
will only be valid if this information has been entered correctly.
The 745 also calculates the total harmonic distortion of the phase current input signals.
The band of frequencies over which this calculation is made can be changed to be more
selective than the default 2
nd
to 21
st
harmonics.
• HARMONIC DERATING FUNCTION: Enter “Enabled” to enable the harmonic derating
factor calculations.
• THD MINIMUM/MAXIMUM HARMONIC NUMBER Enter the minimum/maximum
harmonic number of the frequency band over which total harmonic distortion is
calculated.
5.4.6 FlexCurves™
PATH: SETPOINTS  S2 SYSTEM SETUP  FLEXCURVES  FLEXCURVE A(C)
Three programmed custom FlexCurves™ can be stored in the 745 as FlexCurve™ A,
FlexCurve™ B, and FlexCurve™ C. This allows the user to save special curves for specific
applications and then select them as required for time overcurrent element curves. The
VOLTAGE INCREMENT
PER TAP
0.01 to 20.00 kV in
steps of 0.01
0.001 to 2.000 kV in
steps of 0.001
0.0001 to 0.2000 kV
in steps of 0.0001
Setting Low voltage winding rating value
above 5 kV 1 kV to 5 kV below 1 kV
 HARMONICS [] HARMONIC DERATING
ESTIMATION: Disabled
Range: Enabled, Disabled
MESSAGE
THD MINIMUM HARMONIC
NUMBER: 2nd
Range: 2nd, 3rd, 4th,..., 21st
MESSAGE
THD MAXIMUM HARMONIC
NUMBER: 2nd
Range: 2nd, 3rd, 4th,..., 21st
 FLEXCURVE A [] FLEXCURVE A DELAY AT
1.03 x PU: 0 ms
Range: 0 to 65000 ms in steps of 1
MESSAGE
FLEXCURVE A DELAY AT
1.05 x pu: 0 ms
Range: 0 to 65000 ms in steps of 1
↓
MESSAGE
FLEXCURVE A DELAY AT
20.0 x pu: 0 ms
Range: 0 to 65000 ms in steps of 1